CALIFORNIA 
AGRICULTURAL  EXTENSION  SERVICE 

CIRCULAR  4 

November,  1926 


IRRIGATION  BY 
OVERHEAD  SPRINKLING 


H.  A.  WADSWORTH 


PUBLISHED  BY 

THE  COLLEGE  OF  AGRICULTURE 
UNIVERSITY  OF  CALIFORNIA 


Cooperative  Extension  work  in  Agriculture  and  Home  Economics,  College  of  Agriculture, 
University  of  California,  and  United  States  Department  of  Agriculture  cooperating.  Dis- 
tributed in  furtherance  of  the  Acts  of  Congress  of  May  8  and  June  30,  1914.  B.  H.  Crocheron, 
Director,  California  Agricultural  Extension  Service. 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1926 


Digitized  by  the  Internet  Archive 

in  2011  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/irrigationbyover04wads 


IRRIGATION  BY  OVERHEAD  SPRINKLING 

H.  A.  WADSWOETHi 


INTRODUCTION 

Although  the  irrigation  of  truck  crops  by  overhead  sprinkling  has 
long  been  a  common  practice  in  some  parts  of  the  United  States,  with 
some  citrus  fruits  irrigated  this  way  in  Florida,  the  application  of 
water  by  overhead  sprinkling  has  but  recently  become  a  factor  in 
California  orchard  irrigation  practice.  Though  scattered  installations 
which  have  been  in  operation  for  some  years  are  to  be  found  in  various 
parts  of  the  State,  the  majority  now  in  operation  have  been  established 
since  1924. 

Irrigation  by  sprinkling  is  an  attempt  to  imitate  rainfall.  "Water 
is  carried  in  pipes  under  such  pressure  that  when  released  from 
sprinkler  heads  or  from  perforated  pipes,  the  surface  to  be  irrigated 
is  sprinkled  with  the  coarse  drops  of  a  heavy  shower.  In  details, 
individual  installations  may  differ  widely,  but  in  general,  the  prin- 
ciple is  the  same.  Certain  manufacturers  of  sprinkling  equipment 
recommend  distribution  from  horizontal  pipes  supported  above  the 
surface  of  the  ground  and  equipped  with  non-corrosive  nozzles  or  jets 
at  fixed  intervals  along  them.  Such  an  installation  can  serve  a  zone 
of  a  length  equal  to  that  of  the  pipes  and  of  a  width  determined  by 
the  available  pressure  and  by  the  number  of  lines.  Other  manufac- 
turers recommend  rotary  sprinklers.  When  these  are  used,  sprinkler 
heads  somewhat  similar  in  design  to  revolving  lawn  sprinklers  are  so 
located  in  the  area  to  be  irrigated  that  the  overlapping  circles  of 
application  completely  cover  the  area. 

Sprinkler  equipment  is  relatively  costly  regardless  of  the  type  of 
distributing  system  selected.  Many  installations  which  are  designed 
to  eliminate  all  labor  of  irrigation  except  the  opening  of  a  valve  or 
the  starting  of  a  pump  represent  an  investment  up  to  $300  an  acre. 
Under  favorable  conditions,  when  the  operator  is  willing  to  handle 
some  portable  sprinkling  equipment,  the  initial  cost  may  be  reduced 
to  one-half  of  this  amount  or  less.  When  natural  pressure  is  not 
available  for  the  operation  of  a  sprinkler  installation,  pumps  must  be 
included  in  the  plan.  In  such  cases  the  first  cost  of  the  system  will 
be  increased  by  the  cost  of  the  pump  with  its  fittings,  and  the  annual 


1  Assistant  Professor  of  Irrigation  Investigations  and  Practice  and  Assistant 
Irrigation  Engineer  in  the  Experiment  Station. 


4  CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE  [CiRC.  4 

cost  will  be  increased  by  the   carrying   charges  on   this  additional 
investment  and  by  the  cost  of  the  power  consumed. 

Because  of  the  large  investment  represented  by  sprinkler  equip- 
ment, the  practice  of  overhead  irrigation  has  been  mainly  limited  to 
the  irrigation  of  high-value  crops  on  high-priced  land.  In  California, 
numerous  plantings  of  oranges,  lemons,  avocados,  and  nursery  stock 
are  being  irrigated  by  this  method.  Sprinkling  is  often  practiced  in 
truck-growing  areas  where  soil,  market  facilities,  and  climatic  con- 
ditions warrant  the  expense  involved.  Because  of  the  flexibility  of 
the  system  and  the  possibility  of  irrigating  small  tracts  efficiently 
with  a  minimum  of  labor,  overhead  irrigation  is  rapidly  finding  favor 
with  poultrymen  as  a  means  of  watering  chicken  runs  and  of  irrigat- 
ing small  areas  for  green  feed.  The  method  is  also  sometimes  used  for 
the  irrigation  of  lawns  and  ornamental  shrubs. 


OVERHEAD  SPRINKLER  LINES 

Sprinkler  installations  for  the  irrigation  of  orchards,  nurseries, 
and  truck  gardens  fall  into  two  general  classes:  perforated  overhead 
pipes,  sometimes  called  overhead  nozzle  lines,  and  revolving  sprinkler 
systems  which  water  circular  areas. 

The  distribution  of  irrigation  water  in  the  form  of  small  jets 
forced  through  openings  in  the  shell  of  the  pipe  was  the  first  method 
used.  In  these  early  installations  a  few  lengths  of  pipe  were  per- 
forated and  the  water  forced  through  them  by  a  simple  hand  force 
pump.  Since  these  perforations  were  not  reinforced  with  non-cor- 
rosive metal,  the  holes  gradually  became  irregular  in  sliape  or  entirely 
clogged. 

Modern  sprinkler  lines  carry  patented  nozzles  of  non-corrosive 
material.  These  are  screwed  into  tapped  holes  drilled  through  the 
shell  of  the  pipe.  The  holes  through  these  nozzles  are  intended  to  be 
so  shaped  that  particles  of  rust,  which  may  be  carried  through  the 
pipe,  cannot  clog  them.  It  is  extremely  important  that  the  nozzles  in 
a  pipe  line  be  set  in  a  straight  row.  Special  drilling  machines  have 
been  designed  to  facilitate  this. 

LOCATION  AND  DESIGN  OF  NOZZLE  LINES 

A  strip  of  land  50  feet  wide  can  be  irrigated  from  a  single  over- 
head line  if  that  line  be  so  arranged  that  it  can  be  rotated  through 
a  turning  union  and  the  angle  of  the  jets  changed.  When  the  angle 
of  the  jet  is  45  degrees  above  horizontal,  greatest  distance  is  secured. 
Hence,  the  total  angle  available  in  the  turning  union  should  be  90 


1926] 


IRRIGATION    BY    OVERHEAD    SPRINKLING 


degrees.  Considerable  attendance  is  required  with  installations  of  this 
sort  if  changes  in  angle  of  jet  and  consequently  in  the  area  served 
are  made  by  hand.  Turning  machines  consisting  of  small  turbines, 
driven  by  the  flow  of  water  in  the  vertical  supply  type,  have  been 
devised.  These  attachments  slowly  turn  the  pipe  line  through  the 
required  angle.  Need  for  personal  attendance  is  practically  obviated 
by  the  use  of  this  device. 

The  details  of  the  installations  vary  widely  with  the  proposed  use. 
For  truck  crops  and  ornamental  plantings  the  pipes  may  be  carried 
on  short  posts,  or  even  laid  on  the  ground.  When  the  pipes  are  carried 
on  posts,  these  supports  are  usually  about  15  feet  apart.  When  longer 
spaces  are  used,  it  becomes  increasingly  difficult  to  turn  the  line 
because  of  its  sag.  Simple  roller  bearings  can  be  secured  which  may 
be  placed  on  the  posts  as  an  aid  to  easy  turning.  For  short  lines  the 
bearings  may  be  eliminated  and  the  lines  held  in  place  by  metal  straps 
over  the  tops  of  the  posts.  Even  in  good  installations  with  abundant 
pressure,  lines  longer  than  700  feet  are  not  to  be  recommended. 

Many  growers  object  to  the  obstruction  to  cultivation  which  results 
from  placing  sprinkler  lines  on  short  posts.  Posts  carrying  the  pipe 
lines  about  six  and  one-half  feet  above  the  ground  permit  the  passage 
of  men  and  horses  under  the  lines  and  eliminate  most  of  this  trouble. 
Four  by  four  inch  redwood  posts  make  suitable  supports  for  sprinkler 
lines.  They  should  be  long  enough  to  be  set  in  the  ground  21/2  or  3 
feet  and  should  still  give  a  6I/2  foot  clearance.  When  greater  per- 
manence is  required,  sections  of  IVi-inch  or  li/2-inch  iron  pipe  set  in 
concrete  footings  may  be  used. 

Obstruction  to  cultivation  can  be  still  further  reduced  by  the  use 
of  high  poles  which  may  be  from  100  to  200  feet  apart.  The  nozzle 
line  is  then  suspended  from  a  wire  cable  which  joins  the  tops  of  these 
poles  and  hangs  in  the  form  of  a  catenary  between  them,  the  wires 
supporting  the  nozzle  lines  carrying  specially  designed  galvanized 
iron  hooks  equipped  with  simple  roller  bearings  at  their  lower  ends. 
The  nozzle  lines  fit  into  these  hooks  and  can  be  brought  to  the  proper 
height  by  adjustment  of  the  wires  leading  from  the  supporting  cable. 

Because  of  unavoidable  sag  in  the  cable,  the  height  of  the  poles 
supporting  it  should  be  considerably  greater  than  the  height  required 
for  the  nozzle  line.  Suitable  poles  can  be  made  from  standard  tele- 
phone poles  having  a  diameter  of  8  to  10  inches  at  the  base  and  6  to  8 
inches  at  the  top.  These  poles  should  be  set  in  holes  at  least  6  feet 
deep  and  should  be  tamped  firmly  in  place.  For  greater  permanence, 
footings  of  concrete  may  be  used.  Since  any  deflection  of  the  high 
posts  from  their  original  position  would  result  in  a  further  sagging 


6  CALIFORNIA   AGRICULTURAL   EXTENSION    SERVICE  [CiRC.  4 

of  the  cable  and  a  consequent  distortion  of  the  nozzle  line,  it  is  well 
to  anchor  the  end  posts  with  guy  wires  fastened  to  '  ^  deadmen. ' '  These 
"deadmen''  may  be  any  massive  concrete  or  wooden  members  buried 
3  or  4  feet  below  the  surface  and  attached  to  an  anchor  rod  which 
terminates  in  an  eyebolt  above  the  surface.  The  "deadmen"  should 
not  be  closer  to  the  base  of  the  pole  than  a  distance  equal  to  one-third 
its  height.  Guy  wires  attached  to  these  anchor  rods  by  means  of 
turnbuckles  give  rigid  support  for  the  poles.  Future  sag  in  the  line 
can  be  corrected  by  the  turnbuckles. 

The  weight  of  the  cable  to  be  used  depends  upon  the  spacing  of 
the  poles,  the  length  of  the  pipe  line  to  be  supported,  and  the  pipe 
sizes  which  make  up  that  length.  Most  manufacturers  who  produce 
sprinkling  equipment  of  this  sort  maintain  an  engineering  office  where 
information  as  to  the  suitable  spacing  of  poles  and  the  required  cable 
sizes  can  be  secured.  When  such  advice  is  not  available,  an  engineer 
familiar  with  sprinkling  systems  should  be  consulted  and  his  advice 
followed.  No  detailed  design  of  sprinkler  lines  can  be  given  which 
would  be  suitable  for  common  use,  since  each  installation  must  be 
considered  individually  before  an  intelligent  design  can  be  offered. 
In  general,  the  nozzle  lines  should  be  at  right  angles  to  the  supply 
lines  and  should  run  the  long  way  of  the  area  to  be  irrigated,  in  order 
that  obstruction  to  cultivation  may  be  minimized.  If  the  pipe  sizes 
making  up  the  nozzle  lines  are  wisely  chosen,  and  if  sufficient  pressure 
is  available,  the  lines  may  be  as  far  apart  as  50  feet,  if  necessary  to 
secure  a  better  location  in  the  field. 

The  pipe  sizes  to  be  used  for  overhead  sprinkling  lines  depend 
upon  the  type  of  nozzle  used,  the  pressure  available  at  the  intake  of 
the  line,  and  the  distance  between  nozzles. 

As  has  been  stated  above,  the  overhead  sprinkling  line  finds  its 
greatest  popularity  in  nursery  work,  truck  growing,  and  ornamental 
planting.  The  oldest  installations  in  California  were  of  this  type  and 
were  the  first  ones  used  for  the  irrigation  of  citrus  trees.  The  practice 
of  overhead  sprinkling  did  not  spread  among  citrus  growers,  however, 
because  of  the  obstruction  offered  to  cultural  practices  by  the  sup- 
porting posts.  Horizontal  lines  have  also  proved  a  great  inconvenience 
in  the  handling  of  fumigation  tents.  Furthermore,  it  is  probable  that 
the  fine  stream  issuing  from  a  nozzle  of  the  type  used  on  such  lines 
increases  evaporation  loss.  Figure  1  shows  a  typical  overhead  sprinkler 
line  in  operation. 


^^^^]  IRRIGATION    BY   OVERHEAD    SPRINKLING 


FITTINGS  FOR  NOZZLE  LINES 

In  addition  to  the  special  brass  nozzles  which  are  essential  to  satis- 
factory operation  of  a  sprinkler  installation  of  this  sort,  there  are 
other  fittings  which  reduce  difilculties  of  installation  and  make  for 
greater  convenience  in  operation.  Automatic  turning  equipment  has 
already  been  mentioned,  as  has  also  the  simple  roller-bearing  saddle, 
in  which  a  long  length  of  pipe  may  rest  and  still  turn  easily.  The 
saddle  is  supplied  with  several  base  fittings  for  use  with  various 
methods  of  support  for  the  sprinkler  line.    Turning  unions  completely 


Fig.  1. — General  view  of  overhead  sprinkler  line.  Sprinkling  from  a  perforated 
horizontal  pipe,  which  may  be  rotated  through  a  turning  union,  is  a  popular  means 
of  applying  water  to  ornamental  plants,  vegetables,  and  poultry  runs. 

assembled  are  sold  by  manufacturers  of  sprinkler  equipment.  Ordi- 
narily a  perforated  conical  strainer  is  built  into  the  union  so  that 
water  entering  the  nozzle  line  may  be  kept  free  from  dirt,  which  might 
clog  the  fine  nozzle  openings.  For  extensive  installations  where  several 
parallel  lines  are  to  be  turned  in  unison,  the  power  supplied  by  the 
turbine  of  the  automatic  turning  equipment  is  inadequate  and 
hydraulic  oscillators  may  be  obtained  in  that  case.  The  reciprocating 
action  of  the  central  oscillator  is  carried  to  the  turning  unions  which 
are  operated  by  carefully  balanced  cables. 


8 


CALIFORNIA   AGRICULTURAL   EXTENSION    SERVICE 


[CiRC.  4 


Flushing  valves  are  usually  installed  at  the  end  of  each  nozzle  line 
to  permit  the  removal  of  dirt  and  scale  from  the  line  without  the 
necessity  of  dismantling. 

Difficulty  is  often  experienced  in  assembling  sections  of  drilled 
pipe  since  the  couplings  must  be  tight  and  the  nozzles  in  the  several 
sections  in  perfect  line.  The  use  of  quick-acting  couplings  with 
squared  sockets  makes  it  impossible  to  assemble  the  pipe  unless  the 
nozzles  in  the  several  sections  are  in  perfect  alignment. 


COS 


fe 


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i 


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tiear/ng 


M    >  Jurnina 


>  Turning 
union 


S<H 


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n 


Oofe 
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K-"'i. 


Vi 


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^ 


Fig.  2. — Detail  of  typical  sprinkler  line  assembly.  The  special  fittings  required 
for  the  installation  of  overhead  sprinkler  lines  can  be  secured  only  from  manu- 
facturers of  sprinkling  equipment. 

Other  equipment  such  as  gate  valves,  couplings,  tees,  and  unions, 
which  may  be  necessary  for  assembly,  is  common  to  all  pipe  work  and 
need  not  be  considered.  Figure  2  shows  the  detail  of  a  sprinkler  line 
assembly. 


WATER  REQUIRED  FOR  OPERATION 

For  outdoor  irrigation,  with  nozzles  spaced  on  3-foot  or  4-foot 
centers,  a  supply  of  one  gallon  per  minute  for  every  15  feet  of  line 
should  be  provided.  AVith  uniform  application  over  a  strip  50  feel 
wide,  such  a  flow  would  provide  an  irrigation  of  one  inch  in  about 
eight  hours. 


1926]  IRRIGATION    BY   OVERHEAD    SPRINKLING 


PEESSURE  EEQUIREMENTS 

A  pressure  of  from  25  to  35  pounds  per  square  inch  is  required  at 
the  head  of  a  nozzle  line  for  satisfactory  distribution.  In  cases  where 
this  pressure  is  not  available  or  where  it  cannot  be  created  without 
prohibitive  cost,  special  nozzles  should  be  used  which  are  designed  for 
low  pressure  operation.  Planning  such  a  low  pressure  system  is  a 
special  problem  which  should  be  undertaken  only  under  advice  from 
a  reliable  manufacturer  of  sprinkling  equipment  of  this  sort. 

When  the  sprinkler  lines  are  remote  from  the  source  of  pressure, 
much  more  pressure  is  required  at  the  source  than  can  be  used  at  the 
intake  end  of  the  nozzle  line.  Pressure  is  always  consumed  when 
water  is  forced  through  a  pipe  line.  This  loss  results  in  the  necessity 
of  overcoming  the  resistance  to  flow,  which  is  offered  by  the  relatively 
rough  interior  and  small  diameter  of  the  supply  pipe.  The  amount 
of  pressure  necessary  to  overcome  this  friction  varies  with  the  amount 
of  water  carried,  the  length  of  the  line,  the  size  of  the  pipe,  the 
material  of  the  pipe,  and  its  age.  Methods  of  determining  the  pres- 
sure consumed  under  given  conditions  will  be  discussed  under  a  con- 
sideration of  the  design  of  supply  pipes. 


REVOLVING  SPRINKLER  SYSTEMS 

As  has  already  been  indicated,  sprinkling  heads  cannot  distribute 
water  over  a  given  rectangular  area  as  uniformly  as  a  well  operated 
sprinkler  line  because  of  the  overlap  of  the  circles  of  application 
which  are  necessary  to  insure  complete  coverage.  With  field  crops, 
nursery  plantings,  and  truck  crops,  where  the  location  of  sprinklers 
is  not  rather  rigidly  fixed  by  planting  arrangement,  part  of  this 
objection  can  be  obviated.  When  sprinkler  heads  can  be  located  on 
a  hexagonal  pattern  and  every  head  placed  at  an  equal  distance  from 
every  other  head  adjacent  to  it,  only  about  15  per  cent  of  the  area 
served  will  be  within  the  zones  of  overlap,  provided  the  spacing  is 
properly  determined  according  to  the  spread  which  may  be  expected 
from  a  single  head.  In  cases  where  the  location  of  the  heads  cannot 
conform  to  a  true  hexagonal  spacing  because  of  the  planting  scheme — 
or  for  some  other  reason — the  amount  of  overlap  must  be  increased 
if  complete  coverage  is  provided.  No  real  objection  is  offered  by  this 
necessary  overlap,  since  all  sprinkler  heads  throw  less  water  to  the 
extreme  circumferance  of  the  circle  of  coverage  than  is  applied  to  the 


10  CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE  [ClRC  4 

central  area.     The  overlap  tends  to  equalize  any  lack  of  uniformity 
of  application  which  may  result  from  a  single  head. 

Many  commercial  sprinkler  heads  now  on  the  market  throw  water 
with  fair  uniformity  over  a  circle  with  a  60-foot  diameter  when  a 
pressure  of  from  15  to  18  pounds  per  square  inch  is  available  at  the 
head.  With  an  expected  diameter  of  coverage  of  60  feet,  sprinkler 
heads  should  be  located  so  that  each  head  is  52  feet  from  its  neighbors 
in  every  direction.  Such  a  spacing  can  be  effected  by  staggering  the 
sprinkler  heads  on  feed  lines  which  are  parallel  and  which  are  45  feet 
apart.  This  plan  of  installation  is  evidently  impossible  in  orchards 
that  are  planted  on  the  rectangular  system.  Several  plans  of  layout 
are  shown  in  figure  3.  In  this  figure,  plan  A  is  a  hexagonal  instal- 
lation for  truck  gardens,  nurseries,  or  for  orchards  planted  on  the 
hexagonal  plan.  Plans  B,  C,  and  D  are  superimposed  upon  rect- 
angular orchard  plantings. 


LOCATION  AND  COST  OF  SPEINKLEES  IN  PEEMANENT  PLANTINGS 

In  orchards  set  on  the  rectangular  plan,  with  24-foot  spacings,  a 
close  approximation  to  the  ideal  installation  suggested  above  can  be 
reached  by  establishing  sprinkler  heads  in  alternate  trees  in  alternate 
rows.  When  such  a  scheme  is  adopted,  the  diameter  of  a  single  circle 
of  coverage  must  be  two  and  one-half  times  the  distance  between 
trees,  if  complete  coverage  is  to  be  obtained  with  a  minimum  of  over- 
lap. Under  the  condition  given  the  diameter  of  coverage  required  for 
most  efficient  distribution  is  60  feet. 

Some  growers  object  to  locating  heads  directly  over  a  tree.  The 
accumulation  of  excess  water  at  the  trunk  of  the  tree,  because  of 
unavoidable  leaks  in  the  sprinkler  heads  and  the  difficulty  of  handling 
fumigation  tents  over  trees  equipped  with  sprinkling  stands,  are  given 
as  criticisms  of  this  method.  Growers  who  disapprove  of  such  an 
arrangement  sometimes  install  sprinklers  in  the  centers  of  the  tree 
squares.  The  diameter  of  coverage  required  is  the  same  in  either  case. 
Some  obstruction  to  cultivation  must  be  caused  by  an  installation  in 
which  the  sprinkler  pipes  rise  from  the  centers  of  the  tree  squares. 

Some  types  of  sprinkler  heads  are  designed  for  greater  coverage 
than  the  60-foot  diameter  usually  served  by  the  more  common  heads. 
It  is  difficult  to  use  these  special  heads  advantageously  in  orchards 
on  common  spacings,  because  of  the  unavoidable  overlap  which  must 
be  allowed  to  obtain  complete  coverage.  If  sprinkler  heads  are  placed 
in  every  third  tree  in  every  second  row,  the  circle  of  application  from 
a  single  head  must  have  a  diameter  equal  to  about  three  and  one-third 


1926] 


IRRIGATION   BY   OVERHEAD    SPRTNKIJNG 


11 


Fig.  3. — Typical  layouts  of  permanent  sprinkler  installations, 

A.  A  hexagonal  installation  reduces  the  overlap  of  circles  of  coverage  to  a 
minimum.  Each  head  is  the  same  distance  from  its  neighbors  in  every  direction. 
Such  a  method  of  installation  is  not  adapted  to  orchards  on  a  rectangular  plant- 
ing plan. 

B.  A  common  metliod  of  installation  in  rectangular  plantings  is  to  establish  a 
sprinkler  head  in  every  second  tree  in  every  second  row.  The  sprinkler  heads  are 
not  equally  spaced. 

C.  Economy  in  underground  piping  results  when  individual  sprinklers  can  be 
located  in  every  second  tree  in  every  third  row.  The  distribution  is  lacking  in 
uniformity. 

D.  When  sprinklers  of  large  diameters  of  coverage  are  used  auxiliary  sprinklers 
are  sometimes  installed  to  insure  complete  coverage  without  excessive  overlap. 


12  CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE  [CiRC.  4 

times  the  distance  between  the  trees.  With  trees  planted  on  24-foot 
distances,  for  example,  the  diameter  of  application  required  would  be 
about  80  feet,  and  undesirable  inequalities  in  application  would 
necessarily  result. 

Some  manufacturers,  particularly  those  who  specialize  in  sprink- 
ling devices  for  golf  greens,  offer  sprinklers  wdth  great  diameters  of 
coverage  for  orchard  use.  The  advantage  in  using  such  heads  lies 
in  economy  in  underground  piping.  The  great  disadvantage  is  that 
undesirable  inequalities  of  distribution  must  exist  if  the  sprinkling 
heads  be  located  with  respect  to  existing  tree  rows.  In  some  instal- 
lations with  large-diameter  heads,  a  dry  area  is  allowed  to  remain 
between  the  circles  covered  by  four  large  sprinklers.  This  dry  area 
is  covered  by  a  small  sprinkler  fed  from  a  lateral  leading  from  the 
nearest  main. 

TYPES  OF  SPRINKLEE  HEADS 

Sprinkler  heads  designed  for  orchard  work  fall  into  four  main 
classes,  as  follows : 

(1)  Solid  heads  carrying  no  moving  parts.  With  these,  water  is 
broken  into  drops  by  impact  against  a  baffle  plate  in  the  top  of  the 
head.  The  drops  are  forced  through  ports  in  the  top  or  side  of  the 
head  by  the  pressure  in  the  line.  Such  heads  usually  serve  areas  of 
small  diameter,  their  advantage  being  that  they  have  no  moving  parts, 
which  eventually  necessitate  replacements,  and  that  there  is  freedom 
from  leakage  when  in  operation. 

(2)  Rotary  sprinklers  carrying  small  and  simple  moving  parts. 
These  throw  water  over  a  greater  distance  than  could  be  served  by  a 
solid  head.  This  wider  distribution  may  be  due  either  to  the  impact 
of  a  revolving  member  against  the  jet,  or  to  the  centrifugal  action 
imparted  by  short  arms.  The  pressure  of  the  water  in  the  riser 
revolves  the  moving  parts.  Such  heads  usually  have  a  greater  capacity 
than  solid  heads  and  usually  cover  a  larger  area.  Some  heads  in  this 
class  carry  a  thrust  bearing,  which  is  subject  to  wear.  When  this 
wear  becomes  appreciable,  the  head  leaks  and  the  leakage  runs  down 
the  stand  pipe,  causing  an  undesirable  accumulation  at  the  base.  One 
manufacturer  of  a  popular  head  in  this  class  provides  a  simple  ball- 
bearing to  accommodate  this  thrust  with  a  minimum  of  wear. 

(3)  Long  arm  sprinklers  depending  on  centrifugal  force  for  the 
distribution  of  water.  Arms  of  brass  or  galvanized  iron  pipe  are 
screwed  into  specially  designed  heads,  which  screw  on  the  riser  pipes. 
These  heads  contain  thrust  bearings,  usually  of  babbit  or  monel  metal 
against  brass.     The  arms  are  bent  near  their  outer  ends  so  that  they 


1926] 


IRRIGATION    BY    OVERHEAD    SPRINKLING 


13 


form  a  slight  angle  with  the  diameters  of  the  heads,  as  indicated  by 
the  longer  sections  of  the  arms.  When  water  is  forced  through  these 
arms,  the  reaction  to  the  issuing  stream  causes  the  heads  to  revolve. 
Caps  of  special  design  are  screwed  to  the  ends  of  the  arms  to  promote 
uniform  distribution.  In  many  cases  the  cap  of  one  arm  carries  a 
round  hole  which  throws  a  solid  jet  to  the  extreme  circumference  of 


Fig.  4. — Types  of  sprinkler  heads.  Sprinkler  heads  should  be  selected  after 
consideration  of  the  required  diameter  of  coverage,  the  capacity  of  each  head 
under  the  available  pressure,  and  the  water  supply. 

the  wetted  circle.  The  other  end  sometimes  carries  an  aperture  of 
such  design  that  a  fan-shaped  jet  is  provided,  which  serves  the  inner 
zones  of  the  area.  When  the  arms  of  such  sprinklers  are  of  galvanized 
iron  pipe,  the  bending  to  form  off-set  ends  may  result  in  scales  of 
rust  w^iich  may  lodge  in  the  discharge  orifices  and  stop  the  head. 

(4)   Geared  sprinklers,  designed  to  secure  greater  coverage  than 
can  be  obtained  by  the  common  long  arm  type.    This  end  is  achieved 


14  CALIFORNIA   AGRICULTURAL   EXTENSION    SERVICE  [CiRC.  4 

by  having  part  of  the  water  escape  through  a  central  jet  of  such 
design  that  a  large  throw  can  be  obtained.  The  remaining  water  is 
sent  through  a  rotary  sprinkler  head  which  supplies  the  inner  zones 
of  the  area.  The  rapid  revolution  of  this  rotor  moves  the  large  central 
jet  by  means  of  a  more  or  less  elaborate  gear  train  so  that  the  whole 
circumference  can  be  served.  Many  sprinklers  in  this  group  are 
adjustable  so  that  varying  quantities  of  water  can  be  sent  through  the 
central  jet.  Increasing  the  quantity  discharged  through  the  central 
jet  makes  for  increased  application  on  the  circumference  of  the  circle 
of  coverage  and  a  lighter  application  near  the  center.  Several 
sprinkler  heads  in  common  use  are  shown  in  figure  4. 


UNIFOEMITY  OF  COVEEAGE  FEOM  EEVOLVING   SPEINKLEES 

An  ideal  sprinkler  head  should  apply  water  uniformly  over  the 
diameter  of  coverage.  While  this  ideal  cannot  be  reached,  it  has  been 
approximated  closely  by  several  modern  sprinklers.  When  many 
sprinklers  are  to  be  used  for  the  irrigation  of  a  large  rectangular 
area,  a  slight  ''feathering  out"  in  the  uniformity  of  application  near 
the  circumference  is  not  a  great  disadvantage,  since  the  overlap  of 
these  circles  of  coverage  occurs  on  the  zones  of  lighter  application  and 
tends  to  equalize  them. 

Many  observations  have  been  made  in  an  effort  to  determine  the 
uniformity  of  application  resulting  from  standard  sprinkler  heads  of 
modern  design.  Except  for  solid  heads,  which  are  not  widely  used  in 
orchard  practice,  all  sprinkler  heads  are,  to  some  extent,  adjustable. 
Any  adjustment  tends  to  influence  the  uniformity  of  distribution. 
Light  rotary  heads  can  be  adjusted  by  a  slight  constriction  in  one  or 
all  of  the  small  tubes  through  which  water  is  discharged.  A  slight 
bend  in  the  soft  metal  of  these  tubes  also  affects  the  uniformity  of 
distribution. 

Long  arm  sprinklers  can  be  adjusted  in  two  ways.  One  method 
is  to  change  the  terminal  orifices.  Most  manufacturers  send  long  arm 
sprinklers  into  the  field  with  an  assortment  of  brass  outlet  fittings  to 
be  used  on  the  ends  of  the  arms.  Changing  a  large  holed  fitting  for 
a  small  one  results  in  increasing  the  application  on  the  circumference. 
Equipping  both  ends  of  the  arms  with  such  orifices  in  place  of  fitting 
one  end  with  a  notched  or  diamond-shaped  orifice  results  in  excessive 
application  on  the  circumference  and  almost  no  application  near  the 
center.  Long  arm  sprinklers  can  also  be  adjusted  by  backing  the 
arms  out  of  the  head  so  that  the  angle  formed  by  the  offset  in  the  arm 


1^20]  IRRIGATION   BY   OVERHEAD    SPRINKLING  15 

with  the  horizontal  may  be  changed.  If,  however,  the  arms  are  backed 
out  so  far  that  the  plane  described  by  the  main  part  of  the  arm  and 
the  offset  is  vertical,  there  can  be  no  revolution  and  consequently  no 
distribution. 

As  has  been  mdicated,  geared  sprinklers  can  be  adjusted  by  chang- 
ing the  proportion  of  the  whole  flow  which  passes  through  the  central 
jet.  This  can  be  done  by  the  manipulation  of  a  needle  valve  behind 
the  central  jet,  if  one  is  provided,  or  by  changing  the  brass  orifice  cap 
which  covers  the  jet. 

Changes  in  the  pressure  under  which  a  head  is  operating  may 
affect  the  uniformity  of  distribution  resulting  from  that  head. 

For  these  reasons  it  seems  unnecessary  to  give  results  obtained 
from  distribution  tests.  In  most  cases  heads  must  be  adjusted  after 
installation  to  accommodate  minor  and  perhaps  unintentional  changes 
in  the  head  itself  and  to  adapt  the  head  to  the  pressure  available  at 
the  particular  location.  Tests  for  uniformity  can  be  easily  made  in 
the  field.  In  making  such  a  test  cans  of  uniform  cross-section  are 
placed  at  equal  distances  along  one  radius  of  the  circle  to  be  covered. 
At  the  end  of  a  given  period,  absolute  equality  of  distribution  is 
reflected  by  equal  depths  in  the  several  cans.  Such  a  test  should  be 
run  for  several  hours  before  reliable  conclusions  can  be  reached.  A 
refinement  of  this  method  lies  in  catching  the  water  in  funnels  estab- 
lished at  equal  distances  along  a  radius  and  collecting  the  drainage 
water  from  such  funnels  in  glass  test  tubes  of  equal  diameters.  Minor 
inequalities  of  distribution  are  more  quickly  and  accurately  detected 
by  this  method.  A  day  with  little  or  no  wind  should  be  chosen  for 
such  tests,  since  a  very  slight  breeze  will  result  in  a  great  distortion 
from  the  normal  coverage. 


PEESSURE  EEQUIREMENTS   FOE  EEVOLVING   SPEINKLEES 

Since  the  pressure  under  which  a  sprinkler  head  operates  affects 
its  uniformity  of  distribution,  recommendations  as  to  suitable  pres- 
sures should  be  closely  adhered  to.  Most  solid  and  rotary  sprinklers 
operate  eff'ectively  under  a  pressure  of  15  pounds  per  square  inch  at 
the  head.  Long  arm  sprinklers  require  more  pressure  for  successful 
operation  than  solid  heads.  Geared  sprinklers  ordinarily  require  more 
pressure  for  operation  than  sprinklers  of  any  other  type  because  of 
the  mechanical  losses  in  the  gear  train.  Large  geared  sprinklers,  such 
as  are  used  for  the  irrigation  of  parks  or  golf  greens,  are  sometimes 
designed  for  operation  under  pressures  as  great  as  100  pounds  per 


16  CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE  [CiRC.  4 

square  inch.  Manufacturers  claim  a  diameter  of  175  feet  for  the 
circle  of  coverage  of  geared  sprinklers  under  such  pressures.  The 
pressures  recommended  by  manufacturers  are  usually  those  required 
at  the  heads.  Gages  should  be  installed  at  the  top  of  the  standpipe 
and  immediately  beneath  the  thrust  bearing,  if  the  actual  pressure 
under  which  a  head  is  operating  is  to  be  measured.  If  such  a  location 
is  impracticable,  a  gage  may  be  installed  nearer  the  ground.  If  this 
is  done,  the  reading  on  the  gage  should  be  reduced  by  as  many  pounds 
as  is  represented  by  the  height  of  the  sprinkler  above  the  gage,  divided 
by  2.31.  This  reduced  pressure  will  closely  approximate  the  pressure 
at  the  head. 

CAPACITIES   OF   SPRINKLER   HEADS 

Sprinkler  heads  vary  widely  in  capacities.  This  is  due  partly  to 
differences  in  design  and  partly  to  the  pressures  for  wdiich  various 
heads  may  be  recommended  to  insure  greatest  uniformity  of  distri- 
bution. 

For  heads  commonly  used  for  orchard  irrigation,  such  as  rotary 
sprinklers  and  certain  types  of  long  arm  sprinklers,  a  discharge 
sufficient  to  cover  the  circle  of  coverage  to  a  depth  of  one  inch  in  four 
or  five  hours  may  be  considered  as  typical.  Geared  sprinklers  may, 
and  usually  do,  discharge  more  than  that  indicated  above.  Solid 
heads  of  various  makes  differ  widely  in  discharge  under  operating 
pressures. 

Since  knowledge  of  the  amount  of  water  discharged  by  a  single 
head  is  of  great  importance  in  the  design  of  a  sprinkler  installation, 
tests  have  been  run  on  a  few  modern  heads  under  varying  pressures. 

A  solid  head  popular  in  the  citrus  areas  of  the  southern  states 
was  found  to  discharge  7.6  gallons  per  minute  under  a  pressure  of 
35  pounds  per  square  inch.  Under  a  pressure  of  20  pounds  per  square 
inch,  the  discharge  dropped  to  5.9  gallons  per  minute,  and  10  pounds 
gave  only  3.8  gallons. 

Two  makes  of  long  arm  sprinklers  in  common  use  in  California 
showed  almost  identical  capacities  for  similar  pressures.  These  heads 
discharged  6.9,  5.3,  and  3.8  gallons  per  minute  when  operated  under 
pressures  of  35,  20,  and  10  pounds  per  square  inch,  respectively. 

As  has  been  stated,  geared  sprinklers  have  greater  capacities  than 
either  solid  heads  or  long  arm  sprinklers.  One  geared  sprinkler  used 
in  parks  and  on  golf  greens  discharged  17.3  gallons  per  minute  under 
a  pressure  of  35  pounds  per  square  inch.  Under  pressures  of  20 
pounds  per  square  inch  and  10  pounds  per  square  inch,  the  discharge 
was  13.4  and  9.4  gallons  per  minute,  respectively. 


1926] 


IRRIGATION    BY   OVERHEAD    SPRINKLING 


17 


When  the  discharge  of  a  certain  head  nnder  the  recemmended 
pressure  is  known,  the  time  required  for  an  application  of  one  inch 
of  water  can  be  readily  computed  by  the  following  simple  formula : 

II  D  =  diameter  of  the  wetted  area  in  feet,  and 

G.P.M.  =  capacity  of  the  head  in  gallons  per  minute,  then 

r  P  M  N/  199  ^^  hours  run  required  for  an  application  of  one 
(x.r.M.  X  1--  i^^]^  Qj^  ^j^g  wetted  zone. 

This  equation  is  based  upon  the  assumption  that  evaporation  losses 
are  negligible. 


Fig.  5. — Botary  sprinklers  in  operation.     Permanent  installations  represent 
a  high  first  cost  and  are  most  popular  in  high  producing  areas. 


TYPES  OF  INSTALLATIONS  FOR  USE  WITH  REVOLVING  HEADS 

Permanent  Sprinkler  Installations. — Installations  which  are  pro- 
vided with  fixed  riser  pipes  connected  to  underground  laterals,  are 
sometimes  called  permanent  sprinkler  installations.  Such  an  instal- 
lation is  shown  in  operation  in  figure  5.  AVith  this  type  it  is  possible 
to  irrigate  an  entire  field  or  any  part  of  it  by  an  adjustment  of  the 
valves  which  are  at  the  intake  ends  of  the  laterals  and  in  the  indi- 
vidual riser  pipes.  The  number  of  sprinklers  that  can  be  carried  by 
a  single  lateral,  the  capacity  of  each  head  under  the  available  pres- 
sure, the  topography  of  the  area  to  be  served,  and,  in  some  cases,  the 
head  of  water  available  are  factors  which  affect  the  design.  Since 
these  considerations  vary  widely  in  different  areas,  it  is  inadvisable 
to  copy  an  existing  successful  installation  unless  it  is  definitely  known 


18 


CATJFORNIA   AGRICULTURAL    EXTENSION    SERVICE 


[CiRC.  4 


that  conditions  are  similar.  Every  problem  of  permanent  sprinkler 
design  is  a  special  problem  which  must  be  undertaken  only  after  the 
governing  factors  are  known.  A  typical  plan  for  a  permanent  instal- 
lation is  shown  in  fiefure  6. 


.  SuppfL/  pipe  —. — : .,  J 00  6.PM.  at  60 /hj.  pressure  ^3" 


+     t      f     <-     » — ^-^  »     f — » /  +     f     + — t 
t      -t     ■*-     -f     +      +-'+--1-1/+-     +-     ■♦-,'  + 


+    /  + 
/ 


t     » — r 
+     t     1- 


^^ 


-f — +y  -T     4 

/ 
-h      Y      1-      t 


t? 


*        f       4-V    » 


f       +      /» 


4.A- 


+  '^. 


+     + 


f-— T f   \  4-       T- F ? T ^^ =F r      i-\    + 

+      +      +\4--f-+t       +       +      +      +      +§^ 


■I 


^ TTT T— TT T T T ¥ =T T       +   ^  + 

4        4    '^+        +      \+        -*-        4-        4        ^       4-       +        -u       + 

/  ^ 

rt •-t — ^ • JL      » * ■ — _L      m. — 


^-f- 


4^'.       4      Y 


■^/'. 


/<«7 


Fig.  6. — Typical  plan  for  permanent  installation.  The  pipe  sizes  indicated 
above  are  suitable  only  for  the  conditions  indicated  and  for  installations  in  which 
both  main  and  laterals  are  level.  The  dotted  lines  indicate  the  point  at  whicli 
1-incli  pipe  must  change  to  1^4 -inch  pipe.  Every  installation  is  a  special  problem 
and  must  be  so  considered.  The  circles  represent  coverage  and  indicate  the 
extent  of  overlap. 

It  is  evident  from  the  consideration  of  the  location  of  sprinkler 
heads,  that  laterals  in  the  case  of  permanent  plantings  must  be 
installed  adjacent  to  alternate  rows  in  the  grove,   if  heads  giving 


1^26]  IRRIGATION    BY    OVERHEAD    SPRINKLING  19 

common  diameters  of  coverage  are  to  be  used.  Risers,  capped  by 
sprinkler  heads,  start  from  tees  located  on  the  laterals  below  alternate 
trees.  A  fair  approximation  to  ideal  distribution  can  be  obtained  in 
this  way. 

Six  sprinkling  heads  on  a  single  lateral  are  commonly  used  with 
sprinklers  of  ordinary  capacities.  A  10-acre  area  of  usual  shape 
(Vs  niile  square)  can  be  satisfactorily  irrigated,  if  a  main  pipe  line 
runs  through  the  center  of  the  tract  and  if  laterals  branch  to  each  side 
from  crosses  installed  on  the  main  opposite  the  selected  tree  rows. 
Each  lateral  on  a  10-acre  tract  must  carry  six  risers  to  insure  com- 
plete coverage.  It  is  customary  to  consider  larger  areas  as  multiples 
of  such  units.  In  such  a  case,  the  main  mentioned  above  would  become 
a  lateral  of  the  larger  installation,  while  the  laterals  would  become 
branches  from  laterals  of  the  larger  installation.  Since  available 
water  and  available  pressure  can  rarely  be  developed  for  the  simul- 
taneous operation  of  more  than  10  acres,  the  multiple  installations 
suggested  above  are  very  rare. 

One  of  the  advantages  of  overhead  sprinkling  as  a  means  of  apply- 
ing irrigation  water  is  the  flexibility  of  the  method.  Localized  areas 
of  light  soil  can  be  irrigated  frequently  and  lightly,  while  the  heavier 
soils  can  be  watered  heavily  and  more  infrequently.  Valves  located 
at  the  heads  of  laterals  supplying  water  to  heavy  soils  make  it  possible 
to  cut  out  these  areas  when  water  is  required  by  lighter  soils  under 
the  same  unit.  Globe  valves  may  be  used  for  this  purpose,  although 
simple  cut-off  valves  are  suitable,  since  the  valve  will  usually  be 
entirely  open  or  entirely  closed.  The  valve  in  either  case  will  be 
below  the  surface  of  the  ground,  since  it  must  be  installed  on  the 
underground  lateral.  It  should  be  protected  by  a  short  length  of 
casing  which  ends  at  the  surface  of  the  ground  or  slightly  above  it. 

It  is  practically  impossible  to  select  pipe  sizes  for  a  lateral  with 
such  exactness  that  each  riser  on  that  lateral  will  be  supplied  with  the 
pressure  required  for  best  distribution.  A  small  valve  is  usually 
installed  on  each  riser  so  that  pressures  may  be  equalized  and  each 
sprinkler  head  supplied  with  the  specified  pressure.  In  some  cases 
a  special  fitting,  carrying  a  valve  and  a  strainer,  is  incorporated  in 
each  riser  at  a  convenient  height.  This  fitting  is  so  designed  that  the 
strainer  can  be  cleaned  of  scale  accumulation  and  other  debris  in  the 
water  without  dismantling  the  riser  assembly.  Such  fittings  also 
provide  a  convenient  point  at  which  the  riser  may  be  temporarily 
removed  if  it  interferes  with  fumigation.  Figure  7  shows  a  riser  pipe 
equipped  with  a  strainer  and  valve  fitting. 


20 


CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE 


rClRC.  4 


In  other  installations,  a  strainer  is  built  into  the  head.  Such  a 
design  may  entail  the  use  of  a  ladder  when  the  strainer  is  to  be 
cleaned. 


Fig.  7. — Detail  of  permanent  riser  a8seml)ly.  The  offset  fitting  carries  a 
strainer  and  a  valve  by  which  inequalities  of  pressure  can  be  accommodated.  The 
riser  can  be  dismantled  at  this  fitting  for  cleaning  or  replacement. 

Some  means  of  draining  the  pipe  system  should  be  provided. 
Repairs  and  replacements  can  best  be  made  on  empty  lines.  In  areas 
where  freezing  weather  is  to  be  expected,  lines  should  be  drained. 


1926]  IRRIGATION    BY   OVERHEAD    SPRINKLING  21 

Drain  plugs  should  be  installed  at  the  end  of  each  lateral  and  at  the 
end  of  the  main,  if  local  conditions  would  cause  an  accumulation  of 
water  at  that  point.  Common  plugs  screwed  into  terminal  couplings 
provide  a  cheap  and  satisfactory  means  of  drainage.  In  cases  where 
"the  laterals  run  up  hill  from  the  main,  the  drain  plug  should  be 
installed  in  a  tee  connected  by  a  short  nipple  to  the  discharge  end  of 
the  cut-off  valve  on  that  lateral. 

The  design  of  a  satisfactory  sprinkler  installation  is  complex  and 
requires  considerable  familiarity  with  the  principles  involved  in  the 
flow  of  water  in  pipes.  Some  discussion  of  the  design  of  sprinkler 
layouts  and  a  friction  head  table  for  iron  pipe  of  small  diameters  is 
furnished  in  this  circular  as  an  aid  to  those  who  are  removed  from 
the  service  furnished  by  manufacturers  of  sprinkling  equipment. 

As  may  be  suggested  from  the  list  of  materials  required  for  a 
permanent  sprinkler  installation,  the  cost  of  such  a  system  is  high. 
Under  average  conditions,  when  tree  rows  are  from  20  to  24  feet  apart 
and  when  sprinkler  heads  are  located  in  alternate  trees  along  these 
lines,  a  cost  of  $300  an  acre  is  not  unusual.  This  cost  is  based  upon 
pipe  prices  obtained  in  the  spring  of  1925.  When  truck  crops  or 
nurseries  are  to  be  irrigated  and  a  more  efficient  location  of  sprinkler 
heads  is  effected,  this  cost  may  be  slightly  reduced.  Iron  pipe  has 
the  unfortunate  property  of  an  ever  decreasing  diameter  due  to  the 
formation  of  scale  within  the  pipe.  This  property  is  apparent  even 
when  pipes  carry  only  the  purest  water.  If  an  installation  is  planned 
for  a  20-year  life,  pipe  sizes  which  will  have  ample  capacity  during 
the  whole  period  should  be  chosen.  A  layout  based  upon  the  capacities 
of  new  pipe  might  be  considerably  cheaper  than  the  estimate  given 
above.  The  estimate  of  .$300  an  acre  is  based  upon  a  design  in  which 
the  capacities  of  pipes  ten  years  old  are  considered. 

Portahle  Sprinklers  Operated  from  Underground  Laterals. — Many 
growers  are  prohibited  from  using  a  permanent  installation  because  of 
the  high  first  cost  or  because  of  unwillingness  to  accept  the  high  annual 
overhead  charge  which  such  an  installation  would  entail.  The  use  of 
portable  stands  attached  by  '^^-inch  garden  hose  to  outlets  carefully 
located  on  an  underground  distributing  system  provides  for  the  con- 
venience and  benefits  of  overhead  sprinkling  without  the  high  first 
cost  of  a  permanent  installation. 

There  is  no  standard  design  for  portable  sprinklers.  In  most  cases 
growers  build  sprinkler  stands  from  materials  at  hand  and  cap  them 
with  purchased  sprinkler  heads.  In  some  cases  the  riser  pipe  is 
mounted  on  a  light  wooden  platform  by  means  of  a  bend  elbow.  Guy 
wires  run  from  the  corners  of  the  stand  to  the  top  of  the  riser.    A  tee 


22 


CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE 


[ClRC.  4 


or  elbow  fitted  with  a  hose-tliread  adapter,  allows  for  the  connection 
of  a  supply  hose.  Another  common  type  is  made  entirely  of  pipe 
sections  and  fittings.  A  %-inch  pipe  cross,  fitted  with  3-foot  lengths 
of  %-inch  pipe,  furnishes  the  base.  The  riser  pipe  starts  from  a  tee 
connected  to  one  arm  of  the  cross  by  a  short  nipple.  Three  of  the  arms 
from  the  cross  are  sealed  by  caps,  while  the  fourth  is  fitted  with  a 
hose  thread-adapter  which  allows  the  entrance  of  water.     Guy  wires 


4'x4'  P/ofform 

Fig.  8. — Detail  of  portable  sprinkler  stand.  Such  stands  are  usually  home- 
made except  for  the  sprinkler  head.  The  use  of  a  drop  elbow  at  the  base  of  the 
riser  pipe  simplifies  the  connection  with  the  supply  line. 

are  essential  for  all  types  of  portable  stands.  Figure  8  shows  a  satis- 
factory design  for  a  portable  sprinkler  stand.  Figure  9  shows  such 
stands  in  operation. 

Hose  lengths  used  to  connect  portable  stands  to  underground  out- 
lets should  be  less  than  50  feet  long  because  of  the  great  pressure  losses 
in  such  material.  When  the  hose  is  in  use  short  bends  should  be 
avoided.  Hose  is  at  best  short  lived  and  should  be  carefully  drained, 
coiled,  and  stored  in  the  shade  between  irrigations. 

It  is  evident  that  economy  in  underground  piping  can  be  effected 
by  the  use  of  portable  sprinklers  operated  by  hose  lengths  of  50  feet. 


1926 


IRRIGATION    BY    OVERHEAD    SPRINKLING 


23 


Such  underground  laterals  are  ordinarily  placed  under  every  fifth 
or  sixth  tree  in  the  grove.  The  outlets  are  usually  short  risers,  con- 
nected to  the  underground  lateral  by  means  of  tees,  and  capped  by 


Fig.  9. — General  view  of  portable  sprinklers  in  operation.  The  use  of  such 
portable  sprinklers  reduces  the  first  cost.  Flexibility  in  operation  can  be  gained 
by  the  use  of  such  an  installation. 


24 


CALIFORNIA    AGRICULTURAL    EXTENSION    SERVICE 


[CiRC.  4 


common  garden  faucets  equipped  for  hose  couplings.  Trees  shelter- 
ing such  outlets  are  often  flagged  in  some  way,  to  insure  prompt 
identification  during  irrigation. 

Another  saving  resulting  from  the  use  of  portable  sprinklers  as 
compared  with  permanent  installations  is  in  the  initial  investment 
in  the  risers  and  sprinkling  heads.  Long  arm  sprinklers  which  throw 
relatively  large  quantities  of  water  are  ordinarily  used  on  portable 


60  O.PM. 
^"A        y^^  Pressure 


-H'i 


U" 


/r 


-£" 


d" 


^" 


1^ 


d 


/i 


/r 


vi 


Fig.  10. — Suggested  design  for  underground  pipe  system  under  assumed  con- 
ditions of  available  supply  and  pressure.  Each  sprinkler  is  operated  from  a 
separate  lateral.  Note  the  economy  of  smaller  pipe  necessary  in  this  scheme  of 
installation  as  compared  with  that  shown  in  figure  11. 


sprinklers.  Six  portable  sprinklers  are  usually  operated  at  once,  and 
only  that  number  need  to  be  provided  for  the  usual  10-acre  instal- 
lation. Economy  can  be  gained  by  designing  the  underground  pipes 
so  that  each  lateral  carries  but  one  sprinkler,  rather  than  by  locating 
all  the  sprinklers  along  one  lateral  and  finishing  the  zone  within 
reach  of  that  lateral  before  the  next  is  begun.  With  the  latter  plan 
of  distribution,  the  first  section  of  the  lateral  line  must  be  of  sufficient 


1926] 


IRRIGATION    BY    OVERHEAD    SPRINKLING 


25 


size  to  accommodate  the  water  supply  necessary  for  the  five  sprinl^lers 
below  it  in  addition  to  that  used  by  the  first.  A  further  saving  results 
in  possible  reduction  in  the  diameter  of  the  main  supplying  these 
laterals,  since  the  required  capacity  of  the  main  is  reduced  at  each 
turnout.  Figures  10  and  11  illustrate  the  saving  which  may  be 
effected  by  this  design. 

60  aPM. 


\^//              SO"^  Pressure 

• 

^5" 

a"pipe^ 

e"p/pe^ 

jE^aoh  spnnk/er  ^/Ves 

^\ 

Fig.  11. — Suggested  design  for  underground  pipe  system  for  use  with  portable 
sprinklers  when  eaeli  lateral  must  have  sufficient  capacity  for  the  simultaneous 
operation  of  six  sprinklers. 

Except  for  the  drain  plug  required  at  the  end  of  each  lateral,  few 
fittings  are  needed  for  a  sprinkler  installation  of  this  type.  Valves 
regulating  the  flow  into  the  laterals  may  be  eliminated;  pressure 
adjustment  into  individual  sprinklers  may  be  effected  by  manipulation 
of  the  garden  faucet  serving  the  stand. 

Portable  installations  of  this  type  represent  an  investment  of  about 
$100  an  acre,  including  the  cost  of  the  portable  sprinkling  stands. 
Isolated  installations  in  which  secondhand  pipe  has  been  used  are 
estimated  by  the  owners  to  have  cost  even  less. 


26  CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE  [CiRC.  4 

Portable  Sprinklers  Operated  from  Portable  Surface  Laterals. — 
A  further  decrease  in  cost  can  be  effected  by  the  use  of  portable 
laterals  in  place  of  the  underground  laterals  used  in  permanent  instal- 
lations. Such  installations  are  neither  popular  nor  common,  since  the 
saving  in  cost  by  using  them  is,  to  a  great  extent,  offset  by  the 
increased  labor  cost  of  operation. 

A  main  underground  line  of  sufficient  size  to  carry  the  quantity 
of  water  required  for  the  operation  of  the  portable  stands  is  laid  on 
the  long  axis  of  the  area  to  be  served.  This  line  is  equipped  at 
intervals  of  about  100  feet  with  risers  capped  by  2-inch  hydrants  fitted 
for  connection  to  2-inch  rubber  hose.  A  short  length  of^  such  hose 
furnishes  a  flexible  connection  between  the  hydrant  and  a  portable 
lateral  of  li/2-iiich  pipe,  which  is  assembled  on  the  surface  of  the 
ground  and  which  extends  down  the  center  of  the  zone  to  be  served. 
The  sections  of  pipe  which  make  up  the  surface  lateral  are  fitted  at 
intervals  of  about  sixty  feet  with  3/4-inch  garden  faucets.  Portable 
stands  are  connected  by  means  of  hose  to  these  outlets  in  the  surface 
lateral,  and  a  zone  as  long  as  the  lateral  and  as  wide  as  can  be  reached 
by  the  length  of  hose  used,  is  irrigated  before  the  lateral  is  moved. 
When  one  zone  is  completed,  the  surface  lateral  is  taken  apart,  carried 
to  a  position  opposite  the  next  riser  on  the  main,  and  reassembled. 

It  is  evident  that  the  economy  of  pipe  design  which  is  possible  if 
each  lateral  carries  but  one  sprinkler  cannot  be  effected  with  instal- 
lations of  this  type.  The  main  must  be  large  enough  to  carry  the 
entire  flow  to  its  end;  since  there  is  but  one  lateral,  it  must  be  large 
enough  to  carry  all  the  sprinklers. 


DESIGN   OF   SUPPLY    PIPE   SYSTEMS    FOR   SPRINKLER 
INSTALLATIONS 

Because  of  its  closely  limited  cross-section  and  the  roughness  of 
its  bore,  iron  pipe  offers  appreciable  resistance  to  the  flow  of  water. 
The  smaller  the  pipe  the  greater  is  the  resistance ;  and  if  the  pipe  size 
remains  the  same,  a  greater  resistance  is  offered  to  a  large  flow  than 
to  a  small  one.  The  resistance  to  flow  offered  by  a  pipe  can  best  be 
measured  by  the  loss  in  pressure  which  results  when  water  is  forced 
through  the  pipe.  If  100  feet  of  2-inch  pipe  be  fitted  with  a  pressure 
gage  at  each  end,  and  a  stream  of  water  be  forced  through  that  pipe, 
the  gage  at  the  outlet  end  will  record  less  pressure  than  the  gage  at 
the  inlet  end.  This  loss  of  pressure  measures  the  resistance  offered 
by  the  100  feet  of  2-inch  pipe  to  the  flow  of  the  quantity  of  water 
which  was  forced  through.    If  the  pipe  were  200  feet  long,  the  differ- 


1926] 


IRRIGATION    BY   OVERHEAD    SPRINKLING 


27 


ence  between  the  gage  readings  would  be  twice  as  great.  No  simple 
proportion  exists  between  the  loss  in  pressure  and  the  quantity  of 
water. 

TABLE  1 

Pressure  LO'SSes  in  Pounds  peu  Square  Inch  for  100  Feet  of  Common  Iron 
Pipe  of  Varying  Diameters  and  for  Varying  Flows 


Gallons 

Pipe  sizes  in  inches 

per 
minute 

Va, 

1 

134 

W2 

2 

2H 

3 

3M 

4 

5 

6 

7 

5 

4  55 
6  35 
10.82 
16  45 

1.40 
1.97 
3.38 
5.06 
7.10 
9.52 
12  10 

0.36 
0.52 
0.69 
0.89 
1.86 
2.47 
3.16 
3.94 
4.80 
7.18 
10  16 

6 

8 

0.41 
0.62 
0.87 
1.16 
1.47 
1.83 
2.25 
3.38 
4.75 
6.36 
8.13 
10  00 

10 

0.22 
0.31 
0.41 
0.52 
0.64 
0.78 
1  18 
1.66 
2.21 
2.85 
3.55 
4.29 
6  02 
7.96 
10  25 

12 

14 

0.14 
0.18 
0.22 
0.26 

0  40 
0.56 
0.74 
0.95 
1.19 

1  43 
2.01 
2.68 
3.42 

4  25 

5  51 
7.28 
9.68 

16 

18  . . 

20 

0.10 
0.16 
0.23 
0.31 
0.39 
0.50 
0.60 
0.85 
1  11 
1.42 
1.76 
2.15 
3.06 
3.98 

5  10 

6  40 
7.70 
9  20 

25 

30 

35 

0  14 
0  17 
0.22 
0.26 
0  38 
0.48 
0.63 
0.78 
0.96 
1.34 
1.82 
2  27 
2.72 
3.33 
4  15 
5.02 
5.78 
6  54 
7.70 
9.70 

40 

.. 

45 

50 

0.15 
0.20 
0  27 
0.35 
0.43 
0.53 
0.74 
0.99 
1.26 
1.56 
1.91 
2.25 
2.68 
3.12 

3  55 

4  03 
5.59 
6  91 
8.58 

10  40 

60 

70 

0.09 
0.12 
0.15 
0.18 
0.25 
0.33 
0.42 
0.53 
0.64 
0.76 
0.90 
1.04 
1.20 

1  36 
1.81 
2.34 

2  90 

3  51 

80 



90 

100 



120 

0.10 
0  13 
0.17 
0  20 
0  24 
0.39 
0  36 
0  41 
0  47 
0  55 
0  73 

0  91 

1  09 
1  37 

140 





160 



180 

200 

0.12 

220 

0  14 

240 

. 

0  17 

260 

0  20 

280 

0.23 

300 

0  37 

350 

0.35 

400 

0  44 

450 

0  54 

500 

0  65 

Table  1  is  computed  from  results  of  experiments  compiled  by  Williams  and  Hazen  (Williams, 
Gardner,  S.,  and  Allen  Hazen.  Hydraulic  tables.  3rd  ed.,  revised,  )/5  p.  John  Wiley  and  Sons,  Inc., 
New  York). 

A  value  of  100  has  been  chosen  for  the  "C"  used  in  the  computations  indicated  in  the  table  above. 
The  use  of  this  value  results  in  an  indicated  friction  loss  equivalent  to  the  loss  in  ordinary  iron  pipe 
which  has  been  in  service  for  10  years.  Galvanized  iron  pipe  probably  deteriorates  less  rapidly  than 
common  iron  pipe.  The  friction  losses,  as  given  in  table  1,  are  probably  greater  than  would  be  expected 
in  galvanized  iron  pipe  10  years  in  service. 

Many  engineers  have  endeavored  to  determine  the  pressure  losses 
resulting  when  certain  sizes  of  pipe  are  used  to  convey  varying 
quantities  of  water.  Tables  have  been  prepared  from  numerous 
experiments  by  which  it  is  possible  to  foretell  with  some  degree  of 
exactness  what  losses  in  pressure  may  be   anticipated  under  given 


28  CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE  [CiRC.  4 

conditions  of  diameter  of  pipe,  length  of  pipes,  and  quantity  of  water. 
Table  1  shows  the  pressure  consumed  by  100  feet  of  common  iron 
pipe  of  varying  sizes  when  varying  quantities  of  water,  measured  in 
gallons  per  minute,  are  discharged.  The  loss  resulting  from  other 
lengths  can  be  obtained  by  multiplying  the  loss  as  given  for  100  feet 
by  the  length  of  the  line  in  question,  divided  by  100. 

The  use  of  table  1  makes  it  possible  to  compute  the  pressure 
required  to  force  any  flow  of  water  through  a  line  of  any  length  and 
diameter.  For  instance,  if  a  flow  of  60  gallons  per  minute  is  to  be 
forced  through  a  2-inch  line  300  feet  long,  a  pressure  of  18.06  pounds 
per  square  inch  would  be  consumed  in  overcoming  the  resistance  to 
flow  offered  by  such  conditions.  If  the  water  is  to  be  delivered  at  the 
outlet  under  a  pressure  of  20  pounds  per  square  inch,  an  initial 
pressure  of  38.06  pounds  per  square  inch  would  be  necessary. 

In  designing  sprinkler  layouts,  the  problem  becomes  more  com- 
plicated, for  in  the  main  pipe  line  the  quantity  is  being  constantly 
decreased  as  the  laterals  are  reached.  And  in  the  laterals,  the  flow 
is  being  constantly  reduced  as  successive  sprinkler  heads  are  supplied. 
The  pipe  connecting  the  last  two  sprinkler  heads  on  a  lateral  should 
be  only  large  enough  to  carry  the  quantity  required  for  a  single  head. 
The  section  between  the  main  and  the  first  sprinkler  must  carry  the 
whole  flow  necessary  for  the  lateral. 

There  is  no  short  cut  toward  the  intelligent  design  of  such  instal- 
lation. Each  lateral  must  be  considered  in  turn,  usually  starting  with 
the  one  most  distantly  removed  from  the  source  of  water  and  pressure. 
Pipe  sizes  are  determined  for  each  section  between  successive  sprinkler 
heads.  If  a  manufacturer  recommends,  for  the  sprinkler  head  made 
by  him,  a  working  pressure  of  15  pounds  per  square  inch  then  the  pres- 
sure at  the  foot  of  the  stand  must  be  enough  in  excess  of  15  pounds  per 
square  inch  to  lift  the  water  to  the  top  of  the  stand  and  deliver  it  at 
the  required  pressure.  One  pound  per  square  inch  represents  the 
pressure  exerted  by  a  column  of  water  2.31  feet  high.  If  a  stand  is 
12  feet  high,  the  pressure  at  the  base  of  the  stand  must  exceed  the 
required  pressure  for  the  operation  of  the  head  by  12  divided  by  2.31, 
or  5.2  pounds  per  square  inch.  A  pressure  of  20.2  pounds  per  square 
inch,  as  measured  on  a  gage  at  the  foot  of  the  stand,  would  be  required 
before  satisfactory  operation  could  be  secured. 

The  pipe  joining  this  last  stand  in  the  example  given  above  with 
the  one  next  to  it  must  be  large  enough  to  deliver  the  quantity  of 
water  required  by  a  single  head  through  the  length  of  pipe  repre- 
sented by  the  distance  separating  the  stands,  and  must  provide  a 
pressure  of  20.2  pounds  per  square  inch  at  the  end  of  the  line.     The 


1926]  IRRIGATION    BY   OVERHEAD    SPRINKLING  29 

next  section  must  be  similarly  determined.  In  this  case,  the  quantity 
required  for  two  heads  must  be  considered,  since  the  last  head  and 
the  next  to  the  last  must  be  supplied. 

The  pipe  section  leading  from  the  main  to  the  first  sprinkler  on  a 
line  must  be  laro^e  enough  to  deliver  the  entire  flow  for  the  lateral.  The 
pressure  requirement  at  the  intake  of  this  lateral  must  be  smaller  than 
that  which  is  available  at  the  source,  since  there  is  necessarily  some 
loss  of  pressure  in  the  main  connecting  the  source  of  water  with  the 
head  of  the  lateral. 

Table  2  has  been  prepared  as  an  aid  in  the  determinations  indi- 
cated above.  Certain  hypothetical  conditions  of  pressure  requirements 
and  capacities  of  sprinkler  heads  have  been  assumed  and  possible 
combinations  of  pipe  sizes  computed.  The  pressure  required  at  the 
intake  of  laterals  made  up  of  the  indicated  pipe  lengths  and  carrying 
a  certain  number  of  sprinkler  heads  is  also  given  under  the  heading 
''Initial  Pressure." 

Table  2  can  be  used  only  as  a  rough  guide  to  required  pipe  sizes, 
and  then  only  if  the  distance  between  sprinklers  and  the  capacities 
and  pressure  requirements  are  as  given. 

A  main  designed  to  supply  sufficient  pressure  for  the  most  remote 
lateral  is  usually  large  enough  to  supply  sufficient  pressure  for  nearer 
ones.  Ordinarily  smaller  pipe  sizes  can  be  used  in  laterals  close  to 
the  source  than  in  those  more  distant.  Effort  spent  in  a  close  deter- 
mination of  pipe  sizes,  so  that  every  pound  of  available  pressure  is 
utilized,  is  repaid  by  a  smoothly  operating  system  and  low  first  cost. 

The  design  of  a  system  for  the  use  of  portable  stands  is  less  com- 
plicated than  that  for  a  permanent  installation.  However,  the  same 
principles  apply  and  the  same  care  should  be  used.  The  greatest 
saving  can  be  gained  through  the  careful  design  of  the  main  line,  since 
small  reductions  in  diameters  of  large  sizes  are  reflected  in  relatively 
large  reduction  in  costs  per  foot  of  pipe.  The  principles  involved  in 
designing  the  underground  distributing  main  are,  of  course,  common 
to  all  types  of  sprinkling  installations. 


DEVELOPMENT  OF   PRESSURE    FOR   SPRINKLER   OPERATION 

In  some  limited  areas  irrigation  water  is  delivered  through  pipe 
lines  under  such  natural  pressure  that  sprinkler  installations  can  be 
operated  without  the  use  of  pumps.  Such  conditions,  however,  are 
not  often  found.  Growers  receiving  water  from  gravity  ditches  or 
low  pressure  pipe  lines,  and  those  who  secure  water  from  private 
wells  must  use  pumps  to  supply  the  pressure  necessary  for  sprinkler 


30 


CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE 


[CiRC.  4 


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1926]  IRRIGATION    BY    OVERHEAD    SPRINKLING  31 

operation.  The  cost  of  pumps,  in  such  cases,  must  be  charged  against 
the  sprinkler  installation,  and  the  annual  operation  cost,  including 
interest  and  depreciation,  charged  against  the  maintenance  of  the 
system. 

When  a  pump  is  required  one  of  the  high  pressure  types  should  be 
chosen,  since  the  pressure  at  the  intake  must  be  sufficient  to  overcome 
frictional  resistance  in  the  system  in  addition  to  the  pressure  required 
for  the  operation  of  the  sprinkler  outlets.  Two  types  of  pumps  are 
in  common  use  for  this  purpose,  viz.,  displacement,  or  plunger,  and 
centrifugal  pumps. 

Displacement  pumps  are  those  which  force  water  by  means  of  a 
piston  or  plunger  traveling  backward  and  forward  in  a  close-fitting 
cylinder.  ■  Such  pumps  are  divided  into  several  classes,  depending 
upon  the  number  of  cylinders  built  into  a  single  pump  and  upon  the 
action  of  the  cylinders.  A  single  acting  plunger  forces  water  only  on 
one  stroke  of  the  piston ;  a  double  acting  plunger  forces  water  during 
both  the  forward  and  the  backward  stroke.  All  displacement  pumps 
should  be  equipped  with  ample  air  chambers  to  act  as  cushions  for 
absorbing  pulsations  due  to  the  action  of  the  pistons.  A  relief  valve 
or  by-pass  should  be  placed  in  the  discharge  pipe  to  prevent  damage 
to  the  pump  or  motor,  should  the  discharge  be  shut  off  during  the 
operation  of  the  pump. 

Displacement  pumps  for  sprinkler  operation  should  be  chosen  only 
upon  recommendation  by  reliable  manufacturers  of  pumping  machin- 
ery. For  certain  conditions,  such  as  an  extremely  high  lift  and 
delivery  at  high  pressures,  displacement  pumps  are  well  suited.  Dis- 
placement pumps  cannot  be  used  wdth  waters  carrying  sand. 

Centrifugal  pumps  are  rapidly  gaining  favor  as  sources  of  pres- 
sure for  sprinkler  operation.  When  such  a  pump  is  used,  the  outlets 
can  be  completely  closed  during  the  operation  of  the  pump  without 
damage.  Centrifugal  pumps  create  pressure  by  forcing  water  into  a 
line  by  means  of  an  impeller  or  vaned  wheel  which  revolves  at  a  high 
speed  in  a  closed  shell  or  case.  A  single-stage  centrifugal  pump,  that 
is,  a  pump  which  carries  but  one  impeller,  may  be  used  for  instal- 
lations where  the  required  pressure  at  the  intake  need  not  exceed 
50  pounds  per  square  inch.  In  cases  where  a  greater  initial  pressure 
is  required,  a  two-stage  pump  may  be  used.  A  two-stage  pump  con- 
tains two  impellers,  each  operating  in  a  separate  shell  but  rotated  by 
the  same  shaft. 

Centrifugal  pumps  must  be  installed  close  to  the  source  of  water. 
Long  suction  pipes  should  be  avoided  whenever  possible.  In  cases 
where   a   centrifugal   pump   must   be   placed   directly   over   a  water 


32 


CALIFORNIA   AGRIOULTURAL    EXTENSION    SERVICE 


[CiRC.  4 


supply,  as  in  a  well,  the  distance  from  the  water  level  during  the 
period  of  greatest  draw-down,  to  the  center  line  of  the  pump  must  not 
exceed  22  feet.  All  centrifugal  pumps  must  be  primed  before  start- 
ing. This  can  best  be  accomplished  by  filling  the  suction  pipe  and 
pump  shell  by  means  of  a  priming  pump  located  at  the  highest  point 
on  the  pump's  shell.  Figure  12  shows  a  direct  connected  single-stage 
centrifugal  pump  used  for  the  development  of  pressure  for  sprinkler 
operation. 


Fig.  12. — A  typical  pumping  plant  for  sprinkler  operation.  Such  pumping 
plants  are  necessary  when  the  water  supply  is  not  under  pressure  or  when  available 
pressure  is  inadequate. 


Centrifugal  pumps  are  simple  in  design.  They  are  inexpensive  in 
first  cost,  as  compared  with  displacement  pumps  of  the  same  capaci- 
ties. They  have  few^  wearing  parts  and  are  usually  equipped  with 
adequate  oiling  facilities.  The  better  pumps  are  so  assembled  that 
replacements  may  easily  be  made. 

The  selection  of  the  proper  type  of  centrifugal  pump  and  the 
proper  size  for  a  particular  installation  demands  expert  advice.  The 
efficiency  to  be  gained  by  a  centrifugal  pump  under  any  set  of  con- 
ditions depends  greatly  upon  the  speed  at  which  it  is  operated. 
Recommendations  with  regard  to  the  speed  of  operation  should  be 
carefully  observed. 


1926]  IRRIGATION    BY   OVERHEAD    SPRINKLING  33 


POWER   REQUIREMENTS   FOR  SPRINKLER  OPERATION 

The  power  required  by  any  pumping-  plant  depends  upon  the 
quantity  of  water  lifted  in  a  given  time,  the  height  to  which  it  must 
be  lifted,  or  the  pressure  required  at  the  discharge,  and  the  efficiency 
of  the  plant. 

A  simple  formula  for  determining  the  horsepower  required  for 
lifting  certain  quantities  of  water  to  given  heights  is : 

G.P.M  X  g  X  100  .. 

3960  XJ^  ^^ 

where  G.P.M.  =  quantity  of  water  lifted  in  gallons  per  minute. 
H  ==  vertical  lift  effected,  in  feet. 

E  =  expected   combined   efficiency  of  pump   and  motor. 
(About  65  per  cent  for  well  designed  centrifugal 
plants  driven  by  electric  motors.) 
HP.  =  horsepower  required. 

Since  causing  a  stream  of  water  to  flow  under  a  pressure  of  one 
pound  per  square  inch  requires  as  much  power  as  would  be  expended 
in  lifting  the  same  stream  to  a  height  of  2.31  feet,  the  equation  may 
also  be  written : 

G.PJL  X  f  X  100  ,„. 

^■^■~         1714  X  E  ^^> 

where  P  =  pressure  in  pounds  per  square  inch  which  must  be 

effected  at  the  discharge  end  of  the  pump. 

In  cases  where  the  same  pump  is  used  to  lift  water  through 
appreciable  distances,  as  from  a  well,  and  to  subject  the  discharge  to 
a  pressure  sufficient  to  operate  a  sprinkler  system,  the  motor  must  be 
large  enough  to  satisfy  both  these  demands  for  power.  Such  compu- 
tations can  best  be  made  by  changing  the  pressure  requirements  into 
the  equivalent  feet  of  vertical  lift  (by  multiplying  by  2.31)  and  adding 
the  vertical  lift  to  the  point  to  which  pressure  requirements  are  com- 
puted. The  relation  stated  in  equation  (1)  can  then  be  used.  In 
cases  where  a  long  suction  pipe  is  necessary,  allowances  should  be 
made  for  losses  in  efficiency  due  to  the  resistance  to  flow  in  the  suction 
pipe. 


34  CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE  [CiRC.  4 


THE    EFFECTIVENESS    OF    IRRIGATION    BY   SPRINKLING 

PENETEATION  AND   SOIL  MOISTUEE   CONSIDERATIONS 

The  value  of  overhead  sprinkling  as  a  means  of  irrigation  depends 
upon  the  effectiveness  of  this  method  in  creating  and  maintaining 
a  satisfactory  soil  moisture  content.  Soils  vary  in  water  holding 
capacity  and  permeability,  fine-textured  soils  holding  more  moisture 
than  coarser  soils  but  '' taking"  water  less  readily.  Plants  suffer  for 
water  when  the  moisture  content  within  the  rooting  zone  drops  below 
a  point  known  as  the  wilting  coefficient.  The  wilting  coefficient  for 
most  soils  may  be  determined  in  the  laboratory  with  a  fair  degree  of 
accuracy.  If  it  can  be  assumed  that  the  major  concentration  of  feed- 
ing roots  occurs  in  a  definite  soil  stratum,  a  satisfactory^  method  of 
irrigation  would  permit  the  application  of  water  by  such  a  means 
and  in  such  an  amount  that  the  soil  moisture  content  in*  that  stratum 
of  soil  may  be  maintained  between  these  limits. 

Six  sprinkled  citrus  groves  in  Los  Angeles  and  Orange  counties 
were  sampled  intensively  for  depth  of  penetration  of  irrigation  water 
and  soil  moisture  content  during  the  irrigation  season  of  1925  to 
determine  the  effectiveness  of  irrigation  by  the  sprinkling  method. 
Three  of  these  groves  were  on  decomposed  granite  soils  of  low  water 
holding  capacity  and  easy  permeability,  while  three  were  on  soils  of 
finer  texture  into  which  water  penetrates  less  readily.  In  most  cases 
the  groves  were  sampled  immediately  before  and  after  each  irrigation. 
In  every  case  samples  were  taken  from  the  same  limited  areas  at  each 
time  of  sampling.  Although  this  method  of  sampling  did  not  neces- 
sarily indicate  the  average  moisture  content  in  the  entire  grove  at  the 
time  of  the  sampling,  it  did  give  a  fairly  accurate  idea  of  the  soil 
moisture  history  in  the  small  plots  under  consideration. 

In  the  case  of  the  three  groves  on  decomposed  granite  soils,  the 
sampling  indicated  that  satisfactory  irrigations  had  been  accom- 
plished. In  none  of  these  groves  did  the  soil  moisture  content  in  the 
principal  rooting  zone  fall  below  the  wilting  coefficient  between  March 
and  November.  Adequate  penetration  of  moisture  at  each  irrigation 
was,  in  most  cases,  indicated  by  an  increase  in  soil  moisture  content 
in  the  fourth  foot  of  soil.  The  effect  of  irrigation  was  sometimes 
evident  in  the  fifth  and  sixth  foot.  It  is  to  be  noted  that  these  groves 
were  managed  by  men  experienced  in  sprinkler  operation.  Sprinkler 
heads  were  well  adapted  to  conditions,  and  factors  determining  the 
required  period  of  operation  were  well  understood.    A  great  measure 


1926]  IRRIGATION    BY   OVERHEAD    SPRINKLING  35 

of  the  success  of  overhead  sprinkling  in  these  groves  can  probably  be 
attributed  to  the  experience  of  the  operators. 

Inadequate  penetration  of  irrigation  water  was  noted  in  each  of 
the  three  sampled  groves  on  the  heavier  soil.  In  most  cases  irrigation 
resulted  in  an  increase  in  the  moisture  content  of  the  surface  foot 
alone,  the  greater  depths  being  at,  or  dangerously  near,  the  wilting 
coefficient  when  the  residual  soil  moisture  from  winter  rains  had  been 
depleted  by  plant  withdrawals.  In  one  case,  however,  sprinklers  were 
operated  for  a  period  four  times  as  long  as  usual  and  an  increase  in 
the  soil  moisture  content  was  noted  to  a  depth  of  six  feet.  This  fact 
together  with  scattered  observations  upon  the  penetration  secured  in 
difficult  soils  by  overhead  sprinklers  in  other  areas  seems  to  indicate 
that  adequate  penetration  in  such  soils  can  be  obtained  with  experi- 
ence, patience,  and  proper  care  in  the  selection  and  use  of  equipment. 


DUTY  OF  WATEE 

Observations  on  the  amount  of  water  used  per  acre  in  the  irri- 
gation of  citrus  trees  by  overhead  sprinkling  as  compared  with  the 
amount  used  by  other  methods  show  no  significant  difference  which 
can  be  attributed  to  the  method  of  application.  These  observations 
were  localized  in  three  areas.  In  these  areas  the  amount  of  water  used 
in  1925  on  groves  under  good  sprinkler  management  were  compared 
with  neighboring  groves  of  comparable  age,  variety,  and  thrift,  which 
were  irrigated  by  means  of  furrows.  The  results  of  these  observations 
are  summarized  in  table  3.  Although  it  is  impossible  to  draw  con- 
clusions from  such  a  small  number  of  fields,  it  is  probable  that  in 
practice,  such  factors  as  the  cost  of  water  used,  the  skill  of  the 
irrigator — and  in  the  case  of  surface  irrigation,  the  preparation  of 
the  land — are  of  more  importance  in  determining  the  amount  of 
w^ater  to  be  used  per  acre  than  is  the  method  of  application. 


EVAPOEATION  LOSSES 

Losses  by  evaporation  from  overhead  sprinkling,  especially  during 
periods  of  high  temperatures  and  low  humidity,  are  doubtlessly 
significant  in  areas  where  water  costs  are  high.  As  yet,  no  workable 
means  of  measuring  this  loss  has  been  devised.  Irrigating  by 
sprinklers  at  night  seems  to  reduce  the  losses  from  evaporation. 


36 


CALIFORNIA   AGRICULTURAL    EXTENSION    SERVICE 


[CiRC.  4 


TABLE  3 

Duty  of  Water  in  Acre-Feet  per  Acre  on  Sprinkled  and  Furroay  Irrigated 
Orange  Groves,  Season  1925 


Area 

Soil  type 

h 
■11 

II 
I- 

I  > 

n 
II 

< 

.Hfe 

1 
Weighted 
average 

Sunnyslope  . 

Hanford  gravelly 
sandy  loam. 

1 

8.5 

1.13 

1  13 

1 
2 
3 
4 
5 
6 

4  5 
4  5 
4  5 
10.0 
10  0 
10  0 

1.14 
1  54 
1  75 
1.92 
1  64 
1  71 

1.67 

Sierra  Madre 

Hanford  gravelly 
sandy  loam. 

1 
2 
3 

8.7 

5  0 

23.0 

1  88 
1  26 
1  05 

1.28 

1 
2 
3 

5.50 
4  00 
3,90 

1.42 
1,31 
1.40 

1.38 

La  Canada 

Hanford  gravelly 
sandy  loam. 

1 

8.5 

1.11 

1.11 

1 

10.0 

1.00 

1  00 

FERTILIZER  DISTRIBUTION 

Although  conclusive  experimental  work  is  lacking,  it  can  probably 
be  assumed  that  the  distribution  of  fertilizing  materials  through  the 
soil  after  a  surface  application  may  be  accomplished  more  speedily 
and  more  effectively  by  sprinkling  immediately  after  the  distribution 
of  fertilizer  than  by  any  other  means  except  a  natural  rain  of  proper 
intensity  and  duration. 


PEST   AND   DISEASE   CONTROL 

Experimental  evidence  as  to  effectiveness  of  overhead  sprinkling 
upon  pest  and  disease  control  is  not  available. 


TEMPERATURE  AMELIORATION 

In  areas  affected  by  hot  dry  winds,  relief  from  excessive  drying 
out  can  probably  be  attained  by  sprinkling  during  the  hours  of 
greatest  danger,  since  exaporating  water  absorbs  heat.  An  additional 
benefit  would  accrue  from  the  increased  humidity  in  the  area  under 
the  sprinklers.  In  areas  endangered  by  low  temperatures,  sprinkling 
as  a  means  of  frost  protection  is  of  doubtful  value.  In  freezes  of  long 
duration,  the  ice  load  carried  by  delicate  trees,  when  sprinkling  is 
unwisely  attempted,  may,  and  often  does,  cause  damage  to  the  trees. 


1926]  IRRIGATION    BY   OVERHEAD    SPRINKLING  37 


FEUIT  QUALITY 

Experienced  packing  house  managers  claim  that  fruit  of  a  higher 
quality  comes  from  sprinkled  groves  than  from  groves  irrigated  by 
other  means.  It  has  never  been  proved,  however,  that  the  increased 
quality  is  due  to  the  method  of  irrigation. 


SUMMARY 

1.  Irrigation  by  overhead  sprinkling  is  costly.  At  present  this 
method  of  irrigating  is  limited  to  the  production  of  high-priced  crops 
on  land  of  high  value. 

2.  Intensive  soil-moisture  sampling  during  the  irrigation  season 
of  1925  indicated  that  adequate  soil-moisture  penetration  can  be 
secured  by  the  sprinkling  of  decomposed  granite  and  sandy  loam  soils 
if  the  sprinkling  equipment  is  w^isely  selected  and  intelligently 
operated.  Experimental  evidence  as  to  the  adaptability  of  sprinkling 
to  heavy  soils  is  not  as  conclusive. 

3.  The  type  of  installation  to  be  adopted  for  a  particular  location 
depends  upon  the  crops  to  be  irrigated,  the  money  available  for 
investment  in  such  equipment,  and  the  labor  available  during  the 
irrigation. 

4.  The  detailed  design  of  a  sprinkler  layout  requires  considerable 
skill  and  care. 

5.  Except  in  favored  localities  where  natural  pressure  is  available, 
pumps  must  be  installed  to  create  pressure  for  the  operation  of  the 
system. 

6.  Sprinkler  systems,  if  used,  should  be,  installed  because  of  their 
ability  to  distribute  irrigation  water  uniformly  and  effectively,  and 
not  because  of  claims  for  other  advantages. 

7.  Judgment  and  care  are  essential  in  the  intelligent  operation  of 
a  sprinkler  system.  There  is  no  substitute  for  a  soil  auger  in  deter- 
mining the  effectiveness  of  an  irrigation. 


PUBLICATIONS  AVAILABLE  FOE  FREE  DISTRIBUTION 


BULLETINS 


No.  No. 

253.   Irrigation   and   Soil   Conditions   in  the  366. 

Sierra    Nevada    Foothills,    California. 
2G1.  Melaxuma    of    the    Walnut,     "Juglans  367. 

regia." 

262.  Citrus   Diseases   of   Florida   and   Cuba  368. 

Compared  with   Those  of  California. 

263.  Size   Grades   for  Ripe   Olives.  369. 
268.   Grovring  and  Grafting  Olive  Seedlings. 

273.   Preliminary  Report  on  Kearney  Vine-  370. 

yard   Experimental    Drain.  371. 

275.  The     Cultivation     of     Belladonna     in 

California.  372. 

276.  The   Pomegranate. 

277.  Sudan    Grass.  373. 

278.  Grain    Sorghums.  374. 

279.  Irrigation   of   Rice  in    California. 
283.  The  Olive   Insects  of  California. 

294.   Bean    Culture   in    California.  375. 

304.  A   Study  of  the  Effects  of  Freezes  on 

Citrus    in    California.  376. 

310.   Plum    Pollination. 

312.  Mariout  Barley.  377. 

813.   Pruning      Young      Deciduous      Fruit  379. 

Trees.  380. 

319.   Caprifigs    and    Caprification. 

324.  Storage  of   Perishable  Fruit  at  Freez-  381. 

ing  Temperatures. 

325.  Rice     Irrigation     Measurements     and  382. 

Experiments    in    Sacramento   Valley, 
1914-1919.  383. 

328.   Prune   Growing   in   California. 

331.   Phylloxera-Resistant    Stocks.  385. 

335.   Cocoanut   Meal    as    a    Feed   for   Dairy  386. 

Cows   and    Other  Livestock. 

339.  The    Relative    Cost    of    Making    Logs  387. 

from   Small   and  Large  Timber.  388. 

340.  Control     of     the     Pocket     Gopher     in 

California.  389. 

343.  Cheese    Pests    and    Their    Control.  390. 

344.  Cold    Storage   as    an   Aid  to   the   Mar- 

keting of  Plums.  391. 

346.  Almond    Pollination. 

347.  The  Control  of  Red  Spiders  in  Decid-  392. 

uous  Orchards.  393. 

348.  Pruning  Young  Olive  Trees.  394. 

349.  A     Study    of    Sidedraft    and    Tractor 

Hitches.  395. 

350.  Agriculture      in      Cut-over      Redwood  396. 

Lands. 

352.  Further  Experiments  in  Plum  Pollina-  397. 

tion. 

353.  Bovine   Infectious   Abortion.  398. 

354.  Results  of  Rice  Experiments  in   1922.  399. 

357.  A     Self-mixing    Dusting    Machine    for 

Applying      Dry      Insecticides       and 
Fungicides.  400. 

358.  Black    Measles,     Water    Berries,     and  401. 

Related   Vine  Troubles. 

361.  Preliminary   Yield    Tables    for    Second  402. 

Growth   Redwood.  403, 

362.  Dust  and  the  Tractor  Engine.  404 

363.  The  Pruning  of  Citrus  Trees  in  Cali-  405! 

fornia.  495 

364.  Fungicidal    Dusts    for    the    Control    of 

Bunt. 

365.  Avocado  Culture  in  California. 


Turkish  Tobacco  Culture,  Curing  and 
Marketing. 

Methods  of  Harvesting  and  Irrigation 
in   Relation   of   Mouldy  Walnuts. 

Bacterial  Decomposition  of  Olives  dur- 
ing  Pickling. 

Comparison  of  Woods  for  Butter 
Boxes. 

Browning  of  Yellow  Newtown  Apples. 

The  Relative  Cost  of  Yarding  Small 
and    Large   Timber. 

The  Cost  of  Producing  Market  Milk  and 
Butterfat  on  246  California  Dairies. 

Pear   Pollination. 

A  Survey  of  Orchard  Practices  in  the 
Citrus  Industry  of  Southern  Cali- 
fornia. 

Results  of  Rice  Experiments  at  Cor- 
tena,    1923. 

Sun-Drying  and  Dehydration  of  Wal- 
nuts. 

The   Cold   Storage   of  Pears. 

Walnut    Culture    in    California. 

Growth  of  Eucalyptus  in  California 
Plantations. 

Growing  and  Handling  Asparagus 
Crowns. 

Pumping  for  Drainage  in  the  San 
Joaquin    Valley,    California. 

Monilia  Blossom  Blight  (Brown  Rot) 
of  Apricot. 

Pollination    of    the    Sweet    Cherry. 

Pruning  Bearing  Deciduous  Fruit 
Trees. 

Fig   Smut. 

The  Principles  and  Practice  of  Sun- 
drying  Fruit. 

Berseem  or   Egyptian   Clover. 

Harvesting  and  Packing  Grapes  in 
California. 

Machines  for  Coating  Seed  Wheat  with 
Copper    Carbonate   Dust. 

Fruit    Juice    Concentrates. 

Crop  Sequences  at  Davis. 

Cereal  Hay  Production  in  California. 
Feeding  Trials  with  Cereal  Hay. 

Bark   Diseases   of   Citrus  Trees. 

The  Mat  Bean  (Phaseolus  aconilifo- 
lius). 

Manufacture  of  Roquefort  Type  Cheese 
from    Goat's   Milk. 

Orchard  Heating  in  California. 

The  Blackberry  Mite,  the  Cause  of 
Redberry  Disease  of  the  Himalaya 
Blackberry,    and   its    Control. 

The  Utilization  of  Surplus  Plums. 

Cost  of  Work  Horses  on  California 
Farms. 

The  Codling  Moth  in  Walnuts. 

Farm-Accounting  Associations. 

The  Dehydration  of  Prunes. 

Citrus  Culture  in  Central  California. 

Stationary  Spray  Plants  in  California. 


No. 

87.   Alfalfa. 
117.  The    Selection    and    Cost    of    a    Small 

Pumping  Plant. 
127.   House    Fumigation. 
129.  The   Control  of  Citrus   Insects. 
136.  MeUlotus    indica    as    a    Green-Manure 

Crop  for  California. 
144.   Oidium    or    Powdery    Mildew    of    the 

Vine. 


CIRCULARS 
No. 


157.   Control  of  the  Pear  Scab. 


Lettuce  Growing  in  California. 
Small  Fruit  Culture  in   California. 
The   County  Farm  Bureau. 
170.   Fertilizing     California     Soils    for    the 

1918   Crop. 
173.  The    Construction    of    the    Wood-Hoop 

Silo. 
178.  The  Packing  of  Apples   in   California. 


160 
164 
166 


CIRCULARS—  (Conhnw^d) 


No. 

179.   Factors    of    Importance    in    Producing 

Milk  of  Low  Bacterial  Count. 
190.  Agriculture  Clubs  in  California. 
199.   Onion    Growing   in    California. 

202.  County    Organizations   for   Rural   Fire 

Control. 

203.  Peat   as   a   Manure   Substitute. 

209.  The  Function  of  the  Farm  Bureau. 

210.  Suggestions  to  the  Settler  in  California. 
212.   Salvaging    Rain-Damaged    Prunes. 
215.   Feeding  Dairy  Cows  in  California. 
217.  Methods   for   Marketing  Vegetables   in 

California. 
220.   Unfermented   Fruit  Juices. 
228.  Vineyard  Irrigation  in  Arid  Climates. 

230.  Testing   Milk,    Cream,   and   Skim   Milk 

for  Butterfat. 

231.  The    Home   Vineyard. 

232.  Harvesting    and    Handling    California 

Cherries    for    Eastern    Shipment. 

234.  Winter  Injury  to  Young  Walnut  Trees 

during  1921-22. 

235.  Soil     Analysis     and     Soil     and     Plant 

Inter-relations. 

236.  The    Common     Hawks    and     Owls    of 

California    from    the    Standpoint    of 
the  Rancher. 

237.  Directions  for  the  Tanning  and  Dress- 

ing of  Furs. 

238.  The  Apricot  in  California. 

239.  Harvesting     and     Handling     Apricots 

and  Plums  for  Eastern   Shipment. 

240.  Harvesting    and    Handling    Pears    for 

Eastern   Shipment. 

241.  Harvesting  and  Handling  Peaches  for 

Eastern   Shipment. 

243.  Marmalade  Juice  and  Jelly  Juice  from 

Citrus  Fruits. 

244.  Central  Wire  Bracing  for  Fruit  Trees. 

245.  Vine   Pruning   Systems. 

247.  Colonization    and   Rural   Development. 

248.  Some    Common    Errors    in   Vine  Prun- 

ing and  Their  Remedies. 

249.  Replacing    Missing    Vines. 

250.  Measurement   of   Irrigation   Water   on 

the  Farm. 

252.  Supports  for  Vines. 

253.  Vineyard  Plans. 

254.  The  Use  of  Artificial  Light  to  Increase 

Winter   Egg    Production. 

255.  Leguminous  Plants  as  Organic  Fertil- 

izer   in    California    Agriculture. 

256.  The   Control   of   Wild   Morning   Glory. 

257.  The  Small-Seeded  Horse  Bean. 

258.  Thinning   Deciduous   Fruits. 

259.  Pear  By-products. 

261.  Sewing  Grain  Sacks. 

262.  Cabbage   Growing  in   California. 

263.  Tomato  Production  in  California. 

264.  Preliminary      Essentials      to      Bovine 

Tuberculosis  Control. 


No. 

265.  Plant  Disease   and   Pest   Control. 

266.  Analyzing     the     Citrus     Orchard     by 

Means   of    Simple   Tree   Records. 

267.  The  Tendency  of  Tractors  to   Rise  in 

Front;    Causes   and   Remedies. 

269.  An  Orchard  Brush  Burner. 

270.  A  Farm  Septic  Tank. 

272.  California  Farm  Tenancy  and  Methods 

of  Leasing. 

273.  Saving  the   Gophered   Citrus  Tree. 

274.  Fusarium  Wilt  of  Tomato  and  its  Con- 

trol by  Means  of  Resistant  Varieties. 

276.  Home  Canning. 

277.  Head,    Cane,    and   Cordon   Pruning  of 

Vines. 

278.  Olive  Pickling  in  Mediterranean  Coun- 

tries. 

279.  The  Preparation  and  Refining  of  Olive 

Oil   in    Southern   Europe. 

281.  The  Results  of  a  Survey  to  Determine 

the  Cost  of  Producing  Beef  in  Cali- 
fornia. 

282.  Prevention  of  Insect  Attack  on  Stored 

Grain. 

283.  Fertilizing  Citrus  Trees  in  California. 

284.  The   Almond   in   California. 

285.  Sweet  Potato  Production  in  California. 

286.  Milk  Houses  for  California  Dairies. 

287.  Potato   Production   in   California. 

288.  Phylloxera   Resistant  Vineyards. 

289.  Oak  Fungus  in  Orchard  Trees. 

290.  The  Tangier  Pea. 

291.  Blackhead   and   Other   Causes   of  Loss 

of  Turkeys  in   California. 

292.  Alkali   Soils. 

293.  The    Basis   of   Grape    Standardization. 

294.  Propagation   of   Deciduous   Fruits. 

295.  The   Growing   and   Handling  of   Head 

Lettuce  in   California. 

296.  Control     of     the     California     Ground 

Squirrel. 

298.  The    Possibilities    and    Limitations    of 

Cooperative  Marketing. 

299.  Poultry   Breeding   Records. 

300.  Coccidiosis  of  Chickens. 

301.  Buckeye  Poisoning  of  the  Honey  Bee. 

302.  The   Sugar   Beet   in   California. 

303.  A  Promising  Remedy  for  Black  Measles 

of  the  Vine. 

304.  Drainage  on   the  Farm. 

305.  Liming  the  Soil. 

306.  A  General  Purpose  Soil  Auger  and  its 

Use  on  the  Farm. 

307.  American   Foulbrood   and  its   Control. 


The  publications  listed  above  may  be  had  by  addressing 

College  of  Agriculture, 

University  of  California, 

Berkeley,  California. 


12to-11,'26 


